A number of manufacturing processes attach fasteners having internally threaded bores with open ends, to components by welding. Parts or other components may then be attached to the fasteners using bolts or other externally threaded fasteners in downstream assembly operations.
Examples of such fasteners are the hexagonal nuts indicated in general at 20 in FIG. 1. As illustrated in FIG. 1, each nut features an annular chamfer portion 22a and internal threads 24 formed within the wall of the bore of the nut. The opposite sides of the nuts 20 not visible in FIG. 1 each include a second annular chamfer portion. The nuts are provided with weld projections 26, which are used to weld the nut to a component or part.
Coatings of thermoplastic material, such as fluoropolymer coatings (28 in FIG. 1), are often applied onto the internal threads of the nuts, or other fasteners. As an example only, the thermoplastic material may be TEFLON. The purpose of the fluoropolymer coating is to prevent the build-up of post applied primers, paints and weld spatter on the threads 24 of the fasteners. This prevents fouling of the threads that would otherwise impede downstream assembly operations. The threads are coated up to, and sometimes including, the top (22a) and bottom chamfers that are at the start and the end of the threads 24.
When applying fluoropolymer powders into internally threaded fasteners, such as the nuts of FIG. 1, it is sometimes difficult to prevent the fluoropolymer powder from getting onto the external surfaces of the nuts. This is particularly true when the chamfers must be coated with the fluoropolymer material as well. Thermoplastic material on the exterior surfaces of the fasteners causes paint or primer not to stick and could cause other downstream process problems. In addition, it has been noted that if the projections 26 of the weld nuts get contaminated with the fluoropolymer coating, welding failures and welding equipment damage may result.
Systems and methods for coating the internal threads of fasteners are known. Examples include commonly owned U.S. Pat. No. 5,141,771 to DiMaio et al. and U.S. Pat. No. 5,362,327 to Sessa et al. Each of these patents, however, discloses a nozzle arrangement that uses a fixed vacuum nozzle positioned above a nut opposite a spray nozzle. The fixed vacuum nozzle collects the over-sprayed powder. Such fixed vacuum nozzle designs, however, have limitations with regard to permitting the chamfers to be coating while keeping the outside surfaces of the fastener clean.
In view of the above, a need exists for a method and apparatus that generally prevents the fluoropolymer powder from escaping from the spray zone and getting on the fastener exterior surfaces.
A need also exists for a method and apparatus that provides the option to either coat the top chamfer, the bottom chamfer, neither chamfer or both chamfers of the fastener at the same time.